The invention relates to a dial for an indicating instrument, in particular in a motor vehicle, having an optical conductor as basic body with symbols displayed on its outside, which faces the viewer, for which purpose there is located on the outside a substantially opaque layer which is provided with light passages forming the symbols. Said layer is substantially opaque in this case, because complete capacity can be accomplished technically only with a very high outlay, which is not economically acceptable in mass production. What is important is that the opaque layer and the light passages forming the symbols have a high contrast,
In general, the basic body is produced from an optically conducting material, for example from polycarbonate or PMMA. The outside is flat, and so a previously produced foil which is generally opaque but provided with light passages forming the symbols can be bonded onto the smooth surface.
A plurality of disadvantages arise in this method. Firstly, the shaping option is restricted; specifically, the foil can be bonded only onto a flat surface, in the final analysis. Secondly, the production method is relatively complicated, since the opaque layer must be produced separately as a foil, for example by screening printing. A further disadvantage consists in that it is therefore necessary for two components to be produced and controlled logistically separately from one another.
The invention is based on the problem of creating a dial for an indicating instrument which overcomes the abovenamed disadvantages. It is proposed for this purpose that the basic body be produced by injection molding and that the outside have surface regions with the light passages that are inclined relative to one another.
The limitation of the shaping option is firstly overcome with these features. Depending on their meaning, symbols can respectively be constructed on differently inclined surfaces such that the indicating instrument can be read off more effectively overall. The basic bodies for indicating instruments with light passages are certainly known from the prior art, but the basic body does not serve as optical conductor in them. Moreover, the light passages act only as light sources which illuminate the outsides of the basic body which bear the dial.
A particularly suitable form in which to construct the surface regions inclined relative to one another consists in shaping an inwardly situated annular region and a more outwardly situated annular region, whose outer surfaces respectively form conical surfaces which are inclined relative to one another. Thus, for example, the conical surface of the outer annular region can be steeper than that of the inner annular region. With this shaping, it is possible, for example, to apply the scale for indicating speed to the inwardly situated annular region, whereas further informative markings are present in the outer annular region.
The symbolsxe2x80x94that is to say chiefly the numerals of a speed or rotational speed displayxe2x80x94stand out particularly prominently when they are constructed on raised surfaces of elevations the sides of which are opaque. This produces the impression as if the numerals were floating in front of the background, something which permits a particularly esthetic shaping.
A further advantage of the invention is present whenever the opaque layer is produced on the outer surface. This means that the layer is not produced in advance in a separate production run, for example as adhesive film, but is produced directly by applying opaque material to the basic body. This layer is therefore produced firstly on the basic body. Both methods for applying such a layer are sufficiently known. For example, it is possible to think of applying a surface coating in liquid form or spraying it on as mist.
In this case, in order to produce the light passages, it is possible, firstly, to apply a stencil in advance and remove it after the opaque layer has been applied. Another possibility consists in producing the light passages by removal, for example by thermal or mechanical processing, of the layer in the appropriate regions.
Finally, the way of producing the opaque layer and the production of the basic body by injection molding are in cooperation. A multivarious structure of the dial can be achieved by applying both features. The display possibilities are substantially more versatile than in the case of the method mentioned in the prior art.
In order to couple the light into the basic body, the latter is formed from a disk, preferably a perforated disk, on whose outer surface the symbols are constructed, and from a ring running at right angles thereto, the light being coupled in at the free lower edge of the ring from a light source, for example a light-emitting diode. The light is directed into the disk, advantageously via a reflecting surface in the transition between the disk and ring, and exits through the light passages.
An advantageously particularly high light yield and bright illumination of the symbols results when the side of the basic body opposite the symbols is designed to scatter light.